Is There a Limit to the Size of a Black Hole?

[Keith]

I'm just curious, do black holes have a maximum size? In other words, if it theoretically had an infinite supply of matter to "feed" off of, would the black hole just get more and more massive or is there a point where it can no longer fit anymore matter? Will it just spit out hawking radiation?

 

[mfb]

There is no known size limit.
Larger black holes emit less Hawking radiation.

 

[rootone]

No I don't think there is an upper limit on size, but you can get a situation where the accereted material around a black hole gets so dense that the BH can't absorb it quickly enough.
The excess gets ejected as a high energy beam of particles from just outside the event horizon at the poles of the BH.

 

[Keith]

Awesome, thank you guys

 

[Keith]

Larger black holes emit less Hawking radiation.

That's cool I didn't know that. Why is that?

 

[mfb]

They emit a black-body spectrum with a specific temperature, this temperature corresponds to a wavelength (for light), and that is proportional to their size.
Larger => longer wavelengths => colder => lower intensity of Hawking radiation

 

[George Jones]

That's cool I didn't know that. Why is that?

Don't take what I write below too seriously.

Large black holes produces smaller "tidal forces" at their event horizons than do small black holes. Consequently, at its event, a large black "pulls apart" virtual particle-antiparticle pairs at a slower rate than does a small black hole.

The real analysis is very technical.

 

[Keith]

They emit a black-body spectrum with a specific temperature, this temperature corresponds to a wavelength (for light), and that is proportional to their size.
Larger => longer wavelengths => colder => lower intensity of Hawking radiation

So it's not that bigger black holes emit less hawking radiation than smaller ones? It's just that the surface area becomes more spread out as the black hole becomes larger and is distributed less intensely to an object that remains a constant size? In other words, theoretically, if an object geometrically grew at the same rate as the black hole, would it experience the same amount of hawking radiation the whole time?

Am I understanding correctly? I'm sorry if none of this makes sense. I feel so feeble minded :p

 

[Drakkith]

Well, if you think of a black hole as a perfect black body radiator, then a larger black hole has a lower temperature than a smaller black hole. All known black holes today absorb more energy from the cosmic background radiation, which has the spectrum of a black body at approximately 2.7 kelvin, than they emit in hawking radiation. So while the spectrum of a more massive black hole is that of a cooler body, I don't know how the emitted power scales with black hole mass and size.

 

[Chalnoth]

Well, if you think of a black hole as a perfect black body radiator, then a larger black hole has a lower temperature than a smaller black hole. All known black holes today absorb more energy from the cosmic background radiation, which has the spectrum of a black body at approximately 2.7 kelvin, than they emit in hawking radiation. So while the spectrum of a more massive black hole is that of a cooler body, I don't know how the emitted power scales with black hole mass and size.

Looked it up here:
http://xaonon.dyndns.org/hawking/

Apparently the luminosity in watts scales inversely with the mass squared. So the total energy emitted per unit time is much greater for a smaller black hole.

 

[George Jones]

I don't know if it is useful for his thread, but I gave a "simplified" presentation in

https://www.physicsforums.com/threads/black-hole-temperature-and-entropy.205711/

that includes the power output scaling as the inverse of the mass squared.